This invention relates to a film information recording device for rolled film which is formed with a plurality of exposure areas and a plurality of information recordable areas corresponding to the exposure areas along the longitudinal direction thereof and in which information concerning photography made to each frame is recordable in a corresponding magnetic recordable area.
A novel photosystem such as APS (advanced photo-system) adopts a rolled film in which information (hereinafter, "film information") such as a date of photographing and a print size is magnetically recordable for each frame. The film information is recordable in a strip-shaped magnetic recordable area Fc provided along a longer side of a laterally long exposure area Fa of each frame of a rolled film F as shown in FIG. 13.
According to the novel photosystem, a size L (area length) of the magnetic recordable area is standardized: L=22 mm. This area length L is about two thirds of the length of the longer side of the exposure area Fa. The film information includes a binary data of a specified number of digits, and a bit data "0" or "1" constituting the binary data is magnetically written in the magnetic recordable area Fc by being modulated into a pulse train signal shown in FIG. 14. The pulse train signal shown in FIG. 14 is obtained by allotting two kinds of pulse signals having different duty ratios Du (ty/tx) to the data "0" and "1" and aligning them in time series. In FIG. 14, the pulse signal of Du&lt;50% is allotted to "0" and the pulse signal of Du&gt;50% is allotted to "1".
Further according to the novel photosystem, a recording density Bb (a spatial magnetic displacement per pulse signal) of film information written in the magnetic recordable area Fc and a variation width .DELTA.Bb of the recording density Bb are also standardized.
Since the recording density Bb is determined based on a feed speed vw of the film F during the writing of film information and a write frequency fw (i.e., duration tx of the pulse signal) of the magnetic signal, the feed speed vw, the write frequency fw and a write start timing of film information need to be controlled so as to satisfy the standards of the recording density Bb and its variation width .DELTA.Bb in the camera in accordance with the novel photosystem.
Preferably, it is desirable to start the writing of film information at a moment when a magnetic head reaches the leading end position of the magnetic recordable area Fc and to write the magnetic signal at a constant feed speed vw.
However, since the film information is generally written during the feed of a frame (one frame winding) performed after photography is made to each frame, it is very difficult to feed the film F at a fixed high speed and to precisely start the writing of film information from the leading end position of the magnetic recordable area Fc.
In commercially available cameras in accordance with the novel photosystem, a revolving speed n of a motor as a drive source of the film F during the film winding is detected and the write frequency fw of the magnetic signal during the writing of film information is changed according to this revolving speed n in order to stabilize the film information recorded in the magnetic recordable area Fc.
There are other commercially available cameras in accordance with the novel photosystem in which the variation of the film feed speed vw is reduced by increasing the reduction gear ratio of a torque transmission member for transmitting a torque of a motor to a take-up spool for the film F and reducing the revolving speed of the spool when the film F is wound, thereby suppressing the variation width .DELTA.Bb of the recording density Bb.
Further, in order to stabilize the write start timing of film information, perforations Fb1, Fb2 are formed at the front and rear ends of each exposure area Fa of the film F as shown in FIG. 13, and the positions of the exposure areas Fa and the magnetic recording Fc along longitudinal direction are specified based on the edges of the perforations Fb1, Fb2. Accordingly, the write start timing of film information is generally controlled using a detection signal of the perforation Fb1 in the conventional cameras in accordance with the novel photosystem.
Specifically, in a camera provided with a single optical sensor including a photoreflector for detecting the perforations Fb1, Fb2, the optical sensor is provided in a position of a picture frame toward a film winding chamber (downstream from the film during the film winding) and between the perforation Fb1 of a frame to be exposed in an exposure position and the perforation Fb2 of the previous frame. Upon the start of the film feed, the write start timing of film information in the magnetic recordable area Fc corresponding to the frame to be exposed is controlled in accordance with the detection signal of the perforation Fb1 at the front end of the frame to be exposed which is obtained by the optical sensor. The exposure area Fa of the next frame is controllably stopped in the exposure position (specified position corresponding to the picture frame of the camera) by a detection signal of the perforation Fb2 at the rear end of the frame to be exposed.
The method for changing the write frequency fw of the magnetic signal during the writing of film information according to the revolving speed n of the drive motor for the film F which is adopted in the conventional cameras necessitates a detector for detecting the revolving speed n of the motor as a drive source of the film F and is disadvantageous to the demand for making the cameras smaller and more inexpensive. There may be considered a method for detecting the actual feed speed vw of the film F instead of the revolving speed n of the drive motor. Such a method also necessitates a detector and is accordingly disadvantageous to the demand for making the cameras smaller and more inexpensive.
The method for reducing the revolving speed of the take-up spool stabilizes the winding speed fast since a load at the start of the feed is low. However, this method requires a longer time for the feed of the frame to write the film information, thereby considerably reducing the response performance at the time of continuous photographing and arises a problem in the operability of the camera. In view of this disadvantage, there may be considered a method for controlling the write start timing of film information such that the film information is recorded in an area where the feed speed vw of the film F varies to a smaller extent without considerably reducing the winding speed of the film F. However, according to this method, a recording start position of film information in the magnetic recordable area Fc varies due to a variation of the write start timing of film information from the start of the feed of the film F. If the write start timing is delayed too much, there arises another problem that the film information may not be completely written in the magnetic recordable area Fc.
The conventional method for stabilizing the write start timing of film information is effective for this problem. However, if this method is adopted, it is necessary to balance the stabilization of the write start timing in connection with a feed speed control of the film F so that the feed speed vw of the film F is increased to or above a specified speed at which the film information is recordable at least when the magnetic head passes the front end of the magnetic recordable area Fc. This results in a complicated feed control of the film F during the winding of the film F.
Further, the conventional method for stabilizing the write start timing of film information necessitates a special optical sensor for controlling the write start timing of film information and is accordingly disadvantageous in making cameras smaller and more inexpensive.